One of the biggest questions going into today's primary was whether Rick Santorum's efforts to target Democrats in Michigan's open primary (along with liberal mischief makers) would put him over the top in the state. The early exits suggest nothing special about Democratic turnout in Michigan, but that Santorum's more than three-to-one advantage among those Democrats that did turnout could still put him over the top in a close race.

Ten percent of voters in the Republican primary were Democrats, according to exit polls. That's lower than the 17 percent that turned out in 2000, bolstering Sen. John McCain, R-Ariz., but slightly higher than the seven percent from 2008. Four years ago, there was a competitive Democratic nomination battle, unlike today, and about 600,000 voted in that primary even though it wasn't hotly contested because the Democratic National Committee had punished the state for moving up its primary too early.

But among those Democrats who did vote, Santorum was ahead 50 percent to 15 percent. Do the math, and it means that Democratic voters could give a 3.5 percent boost to Santorum, which could theoretically be the difference if the race turns out to be as close as late polls have suggested.

Of course, Santorum cannot craft a long term strategy around attracting Democrats in GOP contests, as many of the states have closed primaries.